When the sleeve is part of an end fitting on an electrical insulator which has the rod as its insulating component, it will be understood that fixing the sleeve on the rod is an extremely critical operation. If the sleeve is mechanically crimped, the compression must be sufficient to hold the sleeve on the rod, even when a large traction force is applied thereto; yet the compression must not be excessive to avoid damaging the fibers and causing cracking.
U.S. Pat. Nos. 3,152,392 and 3,192,622 and French Pat. Nos. 2 418 960 and 2 447 082 propose inserting the end of the rod into the cylindrical housing of a sleeve whose outside surface may either by cylindrical or else it may be slightly conical or biconical. Crimping is performed by a multi-part polygonal compression matrix for applying inwardly directed radial force on all outside points of the sleeve simultaneously. The desired aim is to multiply the number of matrix parts in order to ensure that the radial force is as uniform as possible.
This method has drawbacks since it causes the sleeve metal to flow perpendicularly to the compression forces in two opposite directions which are symmetrical about a median plane through the compressed zone. This gives rise to traction forces on the rod fibers in two opposite directions. Further, if the compression forces are not uniformly applied along all the generator lines of the sleeve, rod ovalization is observed with layers of fibers shearing apart.
The known method thus damages the fibers in a manner likely to considerably reduce the performance of the insulator in question.
Preferred implementations of the present invention avoid these drawbacks by means of a new method which provides a new type of rod-to-sleeve assembly.